Electromagnetic device having a short circuited turn



H. H. BAKES June 23, 1970 ELECTROMAGNETIC DEVICE HAVING A SHORTCIRCUITED TURN Filed April 4, 196e United States Patent Office 3,517,357Patented June 23, 1970 3,517,357 ELECTRMAGNETIC DEVICE HAVING A SHORTCIRCUITED TURN Hal H. Bakes, Browns Mills, NJ., assignor to HeinemannElectric Company, Trenton, NJ., a corporation of New Jersey Filed Apr.4, 1968, Ser. No. 718,669 Int. Cl. H01h 7/14 U.S. Cl. 335-63 13 ClaimsABSTRACT F THE DISCLOSURE An electromagnetic device comprising asolenoid coil, an armature actuatable iby the coil and a magnetizableIframe carrying the coil. A tube of non-magnetic material within whichis a movable magnetizable core, the tube having a pole piece at one endtoward which the armature is attracted on predetermined overloadconditions, the core being biased toward the end of the tube away fromthe pole piece. A short circuited turn or ring of electricallyconductive, but non-magnetizable material, is associated With the coil,so that the current in the coil required to overcome the bias on thearmature with substantially no time delay, when the gap between the coreand the pole piece is at its maximum, is substantially higher than thecurrent required for a similar device, but which omits the shortcircuited ring.

BACKGROUND OF THE INVENTION This invention relates to electromagneticdevices and, in particular, to circuit breakers and relays in whichoverload sensing is accomplished electromagnetically by a device whichpermits the circuit breaker or relay to actuate after a time delayperiod at certain overloads and with substantially no time delay atother overloads. Such devices are illustrated, for example, in U.S. Pat.No. 2,360;- 922, issued to Kurt W. Wilckens, and U.S. Pat. No.3,329,913, issued to William W. Camp.

'Ihese prior patents relate to an electromagnetic sensing deviceincluding a solenoid coil, a time delay tube housing a movable core ofmagnetizable material movable against the retarding action of a liquidand a pivotal, spring biased, armature to provide a time delay upon theoccurrence of an overload which, if below a certain value and if it doesnot persist for a predetermined time, will not cause the tripping by thearmature of the circuit breakers r operating mechanism and will not openthe circuit breaker contacts, thereby avoiding nuisance tripping. Inthis type of circuit breaker, if the overload current is sufcientlyhigh, the resulting magnetic flux will substantially instantaneouslycause the pivotal armature to pivot and trip the circuit breakeroperating mechanism and will open the circuit breaker contactssubstantially instantaneously, i.e., with no intentional time delay.

However, certain electrical loads may safely accept a very high current,usually an inrush current and a substantially momentary current, i.e.,of very short duration, so that at such currents no tripping of thecircuit breaker may be desired.

Several attempts have previously been made to modify this known type ofelectromagnetic device to permit the flow through the circuit breaker orrelay of higher inrush currents, of short durations, without trippingthe circuit breakers or the relays, as disclosed in U.S. Pat. No.3,307,130, issued to William W. Camp, and U.S. Pat. No. 3,272,934,issued to Normal J. Schwartz et al. It is an object of this invention toprovide another arrangement whereby the electromagnetic device willpermit the flow therethrough of high inrush currents, of shortdurations, without tripping the circuit breakers or the relays.

BRIEF SUMMARY OF THE INVENTION This invention is embodied in anelectrical circuit breaker having separable contacts actuatable by atoggle linkage. The toggle linkage, on predetermined current conditions,is tripped by a pivotal armature. The armature forms part of theelectromagnetic device which further comprises a frame and a solenoidcoil. The solenoid coil partially surrounds a tube housing a core ofmagnetizable material which is biased toward one end, the rear end, ofthe tube. The other, or forward, end of the tube includes a magnetizablepole piece toward which the core moves upon sufficient energization ofthe coil, and the armature is biased away from the pole piece. Adjacentthe armature and the pole piece is placed a short circuited turn or ringin which a current is induced Iby the coil when the current in the coilvaries. The induced current produces a magnetic ilux which delaysactuation of the armature, thus more electrical current will be requiredto produce a sufficient flux (in the gap between the pole piece and thearmature) to attract the armature, i.e., the current level at which thearmature will be actuated substantially instantaneously has been raised,relative to a similar device without a short circuited ring, permittinginrush currents of short duration to flow through the coil withoutcausing tripping of the circuit breaker.

Short circuited turns or rings have been previously disclosed in D.C.relays, to provide a time delay, but, so far as I know, have notheretofore been used in combination with a circuit breaker or relayhaving a tube with a movable core intended to provide a time delay atcertain overloads.

Also, in a D.C. use, a current is induced in the short circuited turn atthe instant the circuit is closed or opened, but not during steady stateconditions. However, for A.C. applications, a current is induced in theshort circuited turn at all times. Although short circuited turns or.shading coils, i.e., slugs or rings, have been previously used in A.C.relays to quiet their operation, one writer, at least, had thought thatthey could not be successfully used to provide a time delay in an A.C.circuit breaker or relay, as it is stated in Relay Engineering byCharles A. Packard, Second Edition, at page 116, as follows:

Slugs may only be used for D-C operation. Where the relay coil operateson alternating current, they would be a tremendous transfer of energyfrom the coil to the slug which would act as a short circuited secondaryon a transformer. Even if this fact is ignored as it might be onapplications where the relay is only energized for extremely briefintervals, the performance of the slug would be erratic when operatingon an A-C relay. This is so because it would merely act to delay thedecay of ux-and the uX through the magnetic parts of an A-C relay variescontinuously depending on the instantaneous value of the current iiowingthrough the operating coil.

In the device which I have invented, the high inrush current usuallyexists for a very short period of time, a few milliseconds, and, thus,the transfer of energy to the short circuited turn takes place at thehigh level of the inrush current for only a very brief time period.Further, should the `high inrush current exceed the level at which thecircuit breaker or relay will trip, or last for a long enough period oftime for the flux to build up to the trip level, such as by movement ofthe core forward, the device will thereafter open and no current willflow through the coil. This is in contrast, for instance, to the normalshaded coil relay, in which the device is normally intended to remainenergized with the armature in the attracted position. That is, in thedevice of this invention, once the armature is attracted, the unit tripsopen, the

3 coil deenergizes, and then the armature is returned to its initialposition by its spring bias.

Also, in my device, the transfer of energy takes place when the magneticcoupling is poorest, i.e., the magnetizable core is in its rearwardmostposition and not coupling the coil and the short circuited turn.

The foregoing and other objects of this invention, the principles ofthis invention, and the best modes in which I have contemplated applyingsuch principles will more fully appear from the following descriptionand accompanying drawings in illustration thereof.

BRIEF DESCRIPTION OF THE VIEWS In the drawings,

FIG. 1 is a side elevation, illustrating a circuit breaker incorporatingthis invention, with a half-case removed to show the general internalarrangement and illustrating the contacts in the closed position;

FIG. 2 is a top view of the solenoid coil and the pole piece taken alongthe line 2-2 in FIG. 1;

FIG. 3 is an enlarged partial, sectional view of the solenoid coil,tube, pole piece, and frame taken along the line 3-3 in FIG. 2; and

FIG. 4 is a partial sectional view similar to FIG. 3, but showing amodification of this invention.

DESCSRIPTION Referring to the drawings, FIG. 1 illustrates a circuitbreaker generally similar to the one disclosed and lclaimed in U.S. Pat.No. 3,329,913, issued to William W. Camp. For a more completedescription of the mechanism of this circuit breaker reference should bemade to the aforementioned patent, but for clarity, the circuit breakermay be brieily described as comprising an insulating case formed byabutting half-cases, only one half-case being illustrated in FIG. 1, anoperating handle 22, and terminals and 26 for connecting the circuitbreaker to a load. Connected to the operating handle 22 is a linkagecomprising toggle links 32 and 34 and a movable arm 36. The terminal 25supports a stationary Contact 38 which cooperates with a movable contact40, the latter being carried by the movable arm 36. The movable arm 36pivots about a pintle 42, carried by a frame 44, and is biased by aspring 46 to the open position ofthe contacts.

The toggle link 34 is pivotally connected to the movable arm 36 at oneend and to the toggle link 32 at the other end to form the knee of thetoggle, the link 32 being pivotally connected at its upper end to thehandle 22 by a pintle 50. The handle 22 oscillates about a fixed pintle52 which is carried by the frame 44 and is biased to the off position ofthe contacts by a reset spring 54, the spring 54 also resetting thetoggle linkage upon tripping of the mechanism.

For locking the toggle in the overcenter position during automaticresetting, the toggle link 32 engages a latch 56 carried by the link 34.

lThe latch 56 is tripped by a pivotal armature 60` having three arms,namely an unlatching member 62, an attracted end 64 and a balanceportion 66. The unlatching mem ber 62 engages the latch 56 and turns itto unlatch the toggle, thereby allowing the toggle to collapse under thebias of the spring 46, when the armature arm 64 is attracted (uponsufficient overload), toward the pole piece 70 of an electromagnet 72.

The electromagnet 72 comprises a solenoid coil 74 about a tube 76, thelatter projecting through a sleeve 77 of a leg 78 of the frame 44 whoseother leg 79 extends longitudinally along the coil, as shown. The tube76 is of non-magnetic material and houses a movable core 80 ofmagnetizable material biased by a spring 82 toward the lower end of thetube and is retarded in its upward movement by a liquid, preferably asilicone oil, within the tube 76 to provide a time delay below certainoverload currents before tripping of the circuit breaker takes place.The coil 74 yhas one end connected to the movable arm 36 by a flexibleconductor 8-4 and the other end connected by a conductor 86 to theterminal. Thus, an electromagnetic tripping device or sensing element isformed by the coil 74, tube 76, movable core 80, and armature 60 fortripping the circuit breaker after a time delay period at certainoverloads or substantially instantaneously at other, higher overloads.

The coil 74 is formed by turns of insulated wire wound around aninsulator bobbing 90 having a central, axial hole through which the tube76 extends. As illustrated, the bobbin 90 has upper and lower flanges 91and 92 and the lower flange 92 may rest upon the leg 78. The tube 76 mayalso be soldered to the leg 78.

The tube 76 extends, at its upper end, as viewed in FIGS. 1 and 3, abovethe upper flange 91 and the pole piece 70 may extend radially beyond theouter, cylindrical wall 94 of the tube to define an annular spacebetween the surface 95 of the pole piece 70 and the upper surfaceA ofthe ange 91 within which is placed a short circuited turn or ring 96 ofnon-magnetizable, but electrically conductive material, such as copper.

It is preferred that the ring 96 extend from the cylindrical wall 94 ofthe tube 70 to the frame leg 79 with a suitable clearance with thecylindrical wall 94 and with the frame leg 79.

Referring to FIG. 4, it has been found that the instantaneous trip pointof a circuit breaker may be further increased if the short circuitedturn or ring 96 is electrically isolated from the tube 76 and the frame44. It is suspected that since one end of the coil 74 is connected tothe movable arm by the exible conductor and, since the frame 44 and thetube 76 are thus at essentially the same eletcrical potential as one endof the coil 74, if the turn or ring 96 is not electrically isolated fromthe tube 76 and the frame 44 an autotransformer effect would be producedwhich is not as effective as an isolated secondary turn. Thus, the ring96 is isolated from the tube 76 by an insulator sleeve 100 which isplaced around the tube 76 between the tube 76 and the pole piece 70',the sleeve 100 having a ange 102 extending radially between the lowersurface of the pole piece 70 and the upper surface of the ring 96. As inthe previous emobidment, the ring 96 is maintained spaced from the frame44.

It has also been found that as the thickness of the short circuited turnor ring increases, i.e., as the mass of the ring increases, theinstantaneous trip point is also raised to a greater extent than wouldbe expected from merely reducing the length of the coil, i.e., by merelyproviding a gap between the upper end of the coil and the pole piece. Itis, of course, assumed that the unit remains otherwise the same, exceptthat the size of the wire for the coil is reduced.

To facilitate commercial production, it may be desired to form the shortcircuited turn or ring by a stacked array of washer-like discs. Thiswould provide a convenient method of providing a short circuited turn ofdifferent thicknesses for different requirements with only one stockpart.

Further, while the short circuited turn or ring has been shown asoccupying substantially all of the available radial space between thetube and the frame, so as to provide as large a volume as possible forany given thickness, it will be understood that the ring need not extendthe entire distance between the tube and the frame to increase to someextent the instantaneous trip point.

Also, while the short circuited turn or ring has been shown aspositioned between the pole piece and the coil, it will understood thatit could be placed above the pole piece or extending in part through thepole piece, although such arrangements would increase the instantaneoustrip point to a lesser extent than if placed as shown in the drawings.Further, while the short circuited member has been shown in the shape ofa ring it is understood that it need not be restricted to a ring shapeto have some iniluence on raising he instantaneous trip point.

Although a frame has been shown in the drawings having a Isleeve 77extending part way into the coil, it will be understood that thisinvention is applicable even where this sleeve is omitted.

Further, this invention has been incorporated in A.C. devices and inD.C. devices which have been successfully tested.

Having described this invention, what I claim is:

1. An electromagnetic device comprising a solenoid coil, an armatureactuatable by said coil, a magnetizable frame about said coil, a tube ofnon-magnetic material surrounded, at least in part, by said coil, amovable and magnetizable core within said tube, means for retardingmovement of said core and biasing said core toward one end of said tube,a magnetizable pole piece secured to the end of said tube opposite tothe end toward which said core is biased and toward which said armatureis movable, said pole piece defining with said core a magnetic gap, saidpole piece defining with said armature another magnetic gap, said corebeing movable by said coil toward said pole piece, further means biasingsaid armature away from said pole piece, and non-magnetizable,electrically conductive means inductively associated with said coil andpositioned adjacent said armature for producing a magnetic liux tendingto delay actuation of said armature, so that the current in the coilrequired to overcome the armature bias with substantially no time delay,at any particular gap between said armature and pole piece, when the gapbetween the core and the pole piece is at its maximum, is substantiallyhigher than the current required for a similar device but which omitssaid conductive means.

2. The structure recited in claim 1 and further including a pair ofseparable contacts, and operating means associated with said armaturefor automatically opening said contacts on predetermined overloads.

3. The structure recited in claim 2 wherein said conductive means isshort circuited.

4. The structure recited in claim 3 wherein said conductive meansconsists of a ring.

5. The structure recited in claim 3 wherein said conductive meanscomprises a plurality of stacked washerlike discs.

6. The structure recited in claim 2 and further including insulationelectrically isolating said conductive means from said tube, pole pieceand frame.

7. The structure recited in claim Z wherein said conductive means isconcentric with said tube and placed between said pole piece and saidcoil at the end portion of said coil adjacent said armature.

8. The structure recited in claim 7 wherein said conductive meansextends radially from said tube to the outer portion of said coil.

9. An electromagnetic device for operating a pair of separable contactscontrolled by an operating mechanism comprising a solenoid coil, amagnetizable frame associated with said coil, an armature attractable bysaid coil, said armature being pivotally carried by said frame, a tubesurrounded, at least in part, by said coil, said tube being ofnon-magnetic material, a pole piece of magnetizable material secured tothe end portion of said tube toward which said armature moves, a core ofmagnetizable material within said tube, a spring biasing said core awayfrom said pole piece and defining a gap, a liquid within said tube forretarding the movement of said core, said magnetizable core beingmovable by the magnetic field of said coil along the longitudinal axisof said coil toward said pole piece, a further spring biasing saidarmature away from said pole piece and defining with said pole pieceanother gap, short circuited non-magnetic ring means inductively coupledto said coil, and positioned intermediate said pole piece and said coiland adjacent said armature for conducting a current in the direction togenerate a magnetic iield opposing the magnetic ield of said coil as thecurrent in the coil varies, whereby the varying current in the coilrequired to overcome the spring bias on the armature with substantiallyno time delay, when the gap between the core and the pole piece is atits maximum, is substantially higher than the varying current requiredto overcome the spring bias on the armature in a similar device butwhich omits said ring means.

10. The structure recited in claim 9 and further including insulationfor electrically isolating said short circuited ring means from saidtube, pole piece and frame.

11. The structure recited in claim 9 wherein said short circuited ringmeans spaces said coil from said pole piece axially along said tube.

12. The structure in claim 11 wherein said frame has two legs one alongthe length of the coil and the other at an angle thereto and throughwhich said tube extends, said coil being disposed between the frame legthrough which said tube extends and said short circuited ring means.

13. An electromagnetic device comprising a solenoid coil, an armatureactuatable by said coil, a magnetizable frame about said coil, a tube ofnon-magnetic material surrounded, at least in part, by said coil, amovable and magnetizable core within said tube, means for retardingmovement of said core and biasing said core toward one end of saidtube,a magnetizable pole piece secured to the end of said tube opposite tothe end toward which said core i's biased and toward which said armatureis movable, said pole piece defining with said core a magnetic gap, saidpole piece defining with said armature another magnetic gap, said corebeing movable by said coil toward said pole piece, further means biasingsaid armature away from said pole piece, and non-magnetizable,electrically conductive means inductively associated with said coil andpositioned around said tube for producing a magnetic ilux tending todelay actuation of said armature, so that the current in the coilrequired to overcome the armature bias with substantially no time delay,at any particular gap between said armature and pole piece, when the gapbetween the core and the pole piece is at its maximum, is substantiallyhigher than the current required for a similar device but which omitssaid conductive means.

References Cited UNITED STATES PATENTS 3/1963 smith 335-39 2/1967 Camp335-236 U.S. Cl. X.R. 335-241

